This invention relates to materials-handling devices normally referred to as stacker cranes, and in particular to stacker cranes having load grasping apparatus capable of transporting a load and storing it in a rack, such as in a warehouse, the rack having a number of storage stations along a narrow aisle.
Previous stacker cranes have generally had limitations in their use of space, especially space in the vertical dimension which is particularly expensive, and also in the dimension perpendicular to the aisles, which is also quite expensive. For instance, patents like Dechantsreiter, U.S. Pat. No. 4,375,936, and Luebke, U.S. Pat. No. 4,538,954, both have fixed and rigid fork-like members which are inserted under the load in its storage position. The cranes disclosed in these patents require that enough room exist between the racks, that is, that the aisles be wide enough, to accommodate the length of the fork-like members in addition to the mast or vertical support structure of the crane. Hence the aisle may have to be substantially wider than the either the mast alone or the load alone.
One solution to this problem has been to split the mast or vertical support vertically into two parts in order to allow the fork-like members to slide between them, effectively allowing the aisles to be narrower, the minimum then being the length of the fork-like members. This solution is disclosed in Reiff, U.S. Pat. No. 4,523,887. This is not a complete solution, however, since the fork-like members must be long enough to safely reach under even the largest load likely to be stored in the rack, with some additional length required for safety. Once again, then, the length of the fork-like members may require the aisle to be wider than the load alone. This basic space inefficiency is inherent in this type of crane.
One solution to this basic space inefficiency is to provide a telescoping shuttle-type crane 1 as shown in FIGS. 1 and 2. The crane 1 shown in those figures includes a vertical mast 2. A crane carriage 3 is raised and lowered along the mast 2 to vertically position a load 4, which rests on a telescoping shuttle table 5. In turn shuttle table 5 rests on the carriage 3. In the apparatus shown, shuttle table 5 has three segments. FIG. 1 shows the shuttle table 5 in the travel position, while FIG. 2 shows the shuttle table 5 in its storage position. As can be seen by comparing these two figures, the load is moved transversely by transverse motion of the segments of the table 5. Higher segments must move further than the lower segments. The disadvantage of this apparatus is that, as the weight of the load 4 is increased, or as the required distance of the transverse motion is increased, the segments of the table 5 and the carriage 3 must be strengthened or the number of segments increased or both. This results in a required increase in the size of the "shuttle window," which is defined as the vertical distance the load 4 is required to be lifted in order to clear any load support means in the rack plus the the vertical distance required to exist between successive loads in order to allow all segments of the shuttle table 5 to be inserted therebetween. Other shuttle mechanisms having similar elements are disclosed in Dechantsreiter et al, U.S. Pat. No. 3,830,379, Klebe, U.S. Pat. No. 4,331,418 and Burt, U.S. Pat. No. 4,428,708.
However, none of the above patents disclose a solution to this last disadvantage, that is, as the size and weight of the load are increased, the load carrying members must be strengthened or reinforced in order to support the additional load. This results in the requirement of a larger shuttle window. For example, for a shuttle crane designed to carry loads up to 40 tons, the shuttle window may have to be increased by up to 30 inches or more solely to accommodate the shuttle table, resulting in a total waste of up to ten to twelve feet or more of the vertical dimension, considering the fact that the height of a rack for stacking loads five high is increased by five times the increase in the shuttle window size. To put it another way, if the shuttle window of each of five vertically arranged storage stations can be reduced by up to 30 inches, there is the possibility that sufficient vertical distance would be cleared for a sixth storage station where there had formerly been only five.
In addition, it may be desirable to have the capability to store the load on support means located at floor level, rather than beginning 30 inches above floor level.
This invention relates to improvements to the apparatus described above and to solutions to the problems raised thereby.